The research described in this proposal seeks to use mutational analysis to elucidate and characterize the transduction pathway(s) whereby yeast cells respond to mating pheromones. Genes involved in pheromone signal transduction will be identified by mutational analysis. Specifically, mutations which allow cells to conjugate in the absence of a pheromone receptor will be selected. These mutations are expected to define downstream elements in the pheromone transduction pathway. Mutations isolated will be used to probe the molecular basis for pheromone signalling. Attempts will be made to order the transduction elements identified with respect to the direction of signal transduction and to determine if the most upstream element interacts directly with the receptor gene products. Mutations isolated will also be used to investigate the role of receptor and pheromone/receptor complexes in the conjugational process. The role of the pheromone receptor in such processes as conjugational chemotropism, receptor downregulation, and desensitization will be assessed. Finally, cloned putative transduction genes will be subjected to sequence analysis in the anticipation that predicted product primary structures will yield information concerning molecular function. Owing to the similar nature of control processes in all eukaryotes, it is certain that what is learned in the course of this investigation will be informative in a general sense.